The present invention relates to the treatment of films comprising a carbon particles based backing layer, and in particular the recycling of wash-water resulting from passing such a film through a wash-tank to remove the said backing layer.
Some films, and especially motion picture films, have antihalation protection in the form of a removable backing layer, comprising a first layer containing carbon particles and a second wax layer The said first layer is obtained by coating a dispersion, in solvent medium, of carbon particles in a soluble binder in an alkaline medium, cellulose acetophthalate. After having played its antihalation protection part, the backing layer is removed, after passing through a prebath in which it is sufficiently softened, by rinsing in a first wash-tank, before development of the film. The rinsing device generally uses water jets whose action can be combined with the action of brushing rollers. The flow rate of these water jets is high (100 1/h to 150 1/h), which causes high water consumption in this treatment step. In addition, the wash-water is charged especially with particles of carbon that are carried off, and has high turbidity and a pH more than 8. Up to now, this wash-water is not usually treated, and is discharged as it is. Whereas, new standards in particular require reduced water consumption for photographic processing and prohibit the discharge of waste water directly into the drains without prior treatment, such as pH adjustment and filtering. One solution to meet these new standards is to prefer wash-water recycling. This means that most of the carbon particles have to have been removed in order to reuse the wash-water with no impact on the film""s sensitometric characteristics. This removal of the carbon particles must be carried out with high efficiency and without damaging the filtering material used.
The present invention provides a treatment method to answer the above-mentioned problems and enable the recycling of the wash-water charged with carbon particles with high efficiency.
The invention provides also a treatment method to enable water consumption to be greatly reduced and to obtain recycled water, which can be used in the treatment process without harming the qualities of the processed film.
The present invention is a method of recycling wash-water resulting from the treatment of a film provided with a carbon particles backing layer, especially comprising treatment in a prebath followed by washing to remove the said carbon particles based backing layer, wherein said method comprises the step of passing said wash-water through an microfiltration unit equipped with a microfiltration membrane made of polytetrafluorethylene-based material, wherein a permeate is obtained, and wash-water free of said carbon particles is obtained in said permeate.
Hereafter, polytetrafluorethylene will be called PTFE.
The method according to the invention enables the removal from wash-water of the carbon particles; the water can then be recycled with high efficiency.